1. Field of the Invention
The present invention relates generally to electronics assemblies and shielded interconnects for electronics assemblies, such as printed circuit boards. More particularly, the present invention relates to shielded interconnect assemblies for RF power amplifier applications. The invention further relates to methods of manufacture of electronics assemblies incorporating interconnects with shields.
2. Description of Related Art
Carefully designed interconnects are needed to transmit an RF signal between two electronics modules or assemblies, such as printed circuit boards. In high powered RF electronics applications, including RF power amplifiers for cellular base stations, a relatively high amount of energy is transmitted through the interconnect. Signal attenuation may occur as a result of radiation of energy into the air or reflections caused by the signal transfer properties of the interconnect. Therefore, one important characteristic of interconnect assemblies is good signal transfer properties with minimal signal attenuation. Other important characteristics are low cost and ease of manufacture.
Conventional methods of avoiding signal attenuation in interconnects include blind mate connector systems, metal ribbon connections, and printed circuit pin and spring socket systems. Each of these approaches has shortcomings which include bulkiness in size, the need for manual labor which increases costs, difficulty in manufacturing, and insufficient shielding.
Furthermore, in conventional RF power amplifier assemblies, it is common to shield electronics modules on a single board with vertical partitions. Such walls, however, require expensive and bulky filters and feed-throughs to allow for electrical communication between the separated modules. Also, it may be desirable to repair certain electronic components without having to interrupt other components which comprise the assembly. The prior art, however, does not provide an effective means for accomplishing this.
For example, one common method of providing an RF shielded interconnection between printed circuit assemblies is to pass a coaxial connector through the shield wall of a printed circuit assembly. A mechanical connection is required as the connector is soldered to the printed circuit assembly. Coaxial pigtails are also employed wherein the center conductor and the shield conductor of a short section of the coaxial cable is hand soldered to the surface of a printed circuit board. The coaxial cable is routed through a hole in the shield wall. In order to provide shielding, however, the shield conductor of the coaxial cable must be mechanically connected to the shield wall through which the conductor passes. Thus, conventional RF interconnections require mechanical connections which are typically performed via manual labor. This increases cost and minimizes potential for automation.
Therefore, what is needed is an interconnect assembly that minimizes signal attenuation through more effective shielding. Furthermore, what is also needed is an electronics assembly that provides rework capability without disrupting the operation of the modules.
The present invention provides structures and methods which overcome the deficiencies in the prior art.
In one aspect, an RF electronics module assembly is provided. The assembly comprises a first printed circuit board, a second printed circuit board disposed, at least in part, in overlapping relation with the first printed circuit board, an interconnect extending from the first printed circuit board and contacting the second printed circuit board, and a conductive gasket disposed between the first printed circuit board and the second printed circuit board and surrounding the interconnect, the gasket contacting the first printed circuit board and the second printed circuit board. The conductive gasket comprises a conductive material placed on the second printed circuit board. The gasket may be placed on the second printed circuit board by printing, dispensing, or using a variety of other methods. The conductive gasket provides a continuous RF seal around the portion of the interconnect between the upper printed circuit board and the lower printed circuit board.
The first printed circuit board preferably comprises a lower surface having a ground plane in contact with the conductive gasket. The second printed circuit board preferably comprises a connector board with an upper surface having a ground plane in contact with the conductive gasket. The second printed circuit board further comprises a top ground plane, an RF transmission layer, and a bottom ground plane. The interconnect is electrically coupled to the RF transmission layer of the second printed circuit board. The conductive gasket may further comprise a plurality of apertures adapted for receiving a plurality of DC signal pins.
In another aspect, an RF electronics assembly is provided wherein multiple printed circuit boards are coupled to a connector printed circuit board. The assembly comprises a connector printed circuit board, which comprises a lower printed circuit board in a preferred embodiment. A first upper RF shielded enclosure including a first electronics module is coupled to the connector printed circuit board with a first interconnect extending from the first electronics module to the connector printed circuit board. A first conductive gasket surrounds the first interconnect between the first electronics module and the connector printed circuit board. A second upper RF shielded enclosure including a second electronics module is coupled to the lower printed circuit board with a second interconnect extending from the second electronics module to the lower printed circuit board. A second conductive gasket surrounds the second interconnect between the second electronics module and the lower printed circuit board. The first upper RF shielded enclosure further comprises a first lid covering the first electronics module. The second upper RF shielded enclosure further comprises a second lid covering the second electronics module. The first interconnect is disposed between and in contact with the first electronics module and the lower printed circuit board. The second interconnect is disposed between and in contact with the second electronics module and the lower printed circuit board. The first conductive gasket and the second conductive gasket comprise conductive material placed on the lower printed circuit board.
A method of manufacturing an electronics module assembly is also provided. The method comprises providing an upper printed circuit board, providing a lower printed circuit board, electronically coupling the upper printed circuit board to the lower printed circuit board with an interconnect, disposing a conductive gasket in between the upper printed circuit board and the lower printed circuit board, and surrounding the interconnect with the conductive gasket so as to provide RF shielding of the interconnect.
Disposing a conductive gasket in between the upper printed circuit board and the lower printed circuit board preferably comprises contacting the upper printed circuit board and the lower printed circuit board with the gasket and providing a compressive force to the gasket via the circuit boards. Providing an upper printed circuit board preferably comprises forming a ground plane on a bottom surface of the upper printed circuit board. Providing a lower printed circuit board comprises forming an upper ground plane, a middle RF transmission layer, and a lower ground plane. Disposing a conductive gasket in between the upper printed circuit board and the lower printed circuit board preferably comprises placing conductive material on the lower printed circuit board.
A method of assembling an RF power amplifier assembly is also provided. The method comprises electronically coupling a first electronics module to a lower printed circuit board with a first interconnect, covering the first electronics module to provide RF shielding, electronically coupling a second electronics module to the lower printed circuit board with a second interconnect, covering the second electronics module to provide RF shielding; RF shielding the first interconnect, and RF shielding the second interconnect. Covering the first electronics module to provide RF shielding comprises covering the first electronics module with a first removable lid. Covering the second electronics module to provide RF shielding comprises covering the second electronics module with a second removable lid. RF shielding the first interconnect comprises surrounding the first interconnect with a first gasket. RF shielding the second interconnect comprises surrounding the second interconnect with a second gasket. The method further comprises placing conductive material on the lower printed circuit board to form the first gasket and the second gasket.
In summary, an electronics assembly incorporating an interconnect includes a conductive gasket disposed between a first printed circuit board and a second printed circuit board. The gasket surrounds, and thereby shields, the interconnect while providing an RF ground connection between the two boards with a controlled RF impedance. The second printed circuit board may serve as a connector board for a plurality of modules, or other printed circuit boards, to be coupled thereto. Each module is individually covered with a separate lid. Methods for manufacturing and assembling structures according to the invention are also provided.
The invention, now having been briefly summarized, may be better appreciated by the following detailed description.